1. Field of the Invention
Methods consistent with the present invention relate to broadcast encryption, and more particularly, to a method of tracing a device key in a user key management system for broadcast encryption.
2. Description of the Related Art
Broadcast encryption is an efficient method for a transmitter, that is, a broadcast center, to transmit information to desired users from among all the users, and can be used efficiently when a group of users who will receive information is arbitrary and is dynamically changed. The most important characteristic of the broadcast encryption is to revoke a device key of an undesired user, for example, an illegal user, i.e., an unauthorized user, or an expired user, that is, to remove the device key from a broadcast encryption system.
A hierarchical hash chain broadcast encryption scheme (HBES) algorithm is one of the broadcast encryption methods. Also, it is inefficient in that a conventional method of tracing a device key is applied to the HBES algorithm and thus an efficient method of tracing a compromised device key is required.
Conventionally, only a broadcast encryption (revocation) algorithm using a one-way hash chain exists. Thus, when a key set is exposed or when illegal devices, i.e., unauthorized, are distributed due to cloning, there is no tracing method afterward.